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Calibration Techniques and Challenges in the S3/S4 Gravitational Wave Observatories

This document details calibration processes and innovations in the S3/S4 gravitational wave detector runs, featuring insights from key researchers such as Peter Fritschel and Gabriela González. The first version of the S3 calibration, released on January 28, 2005, introduced demodulated lines for alpha and beta estimates. It addresses issues like measurement errors, online calibration challenges, and the employment of a photon calibrator. Insights into expected precision and accuracy, alongside problems encountered during calibration, are discussed along with preliminary modeling results.

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Calibration Techniques and Challenges in the S3/S4 Gravitational Wave Observatories

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  1. S3/S4 Calibration A cast of thousands… including Peter Fritschel, Gabriela González, Corey Gray, Mike Landry, Greg Mendell, Brian O’Reilly, William Quintero , Rick Savage Xavier Siemens, Myungkee Sung, Patrick Sutton, Rai Weiss…

  2. S3 Calibration • S3 Final calibration V3: released Jan 28 2005. • First version to use “demodulated” lines for alpha, beta estimates (X. Siemen’s code). • Also, first science run to use “dynamic beta”. • Somewhat reviewed (?) • Document, paper with details and errors in preparation. • Measurement errors in alpha, beta <0.5%, DC calibration ~few-10%, reference functions ~few %, 5o • new flag CALIB_LINE_V03 (supersedes all the old flags, except no EXC).

  3. S4 calibration • Two gw channels, with different (but related!) calibrations: • DERR(t)=b(t) ASQ(t); CDERR(f)=k0CASQ(f) • AS_Q, with h(f)=RASQ(f,t) ASQ(f) and RASQ(f,t)=(1+a(t)b(t)G(f))/(a(t)CASQ(f)) • DARM_ERR (“darma”), with h(f)=RDERR(f,t) DARM_ERR(f) and RDERR(f,t)=(1+a(t)b(t)G(f))/(a(t)b(t)CDERR(f))

  4. S4 online calibration • Released ~ a week before S4 (a first!) • Not reviewed yet (errors?) • Online coefficients (OLOOP_GAIN, CAV_FACTOR) from SenseMon • Problems: Dropouts • Recommend: use DARM_ERR with a(t)*b(t)=1.

  5. S4 to-do list • A few more measurements (electronics, cavity poles,…) • DC vs AC calibration, sign of calibration • Revised model and reference functions • Coefficients from demodulated lines (M. Sung) -- ~a week after S4 • Error estimates • DQ flags (dropouts, large fluctuations, large errors…) • H1 Photon calibrator: validation

  6. S4 photon calibrator • previously installed and tested – laser troubles with rotating polarization • recently reinstalled at LHO (Corey Gray) on new LLO-designed shelves (Oddvar Spjeld) Expectations: photon calibration would be precise but not necessarily accurate (~20%?). Official calibration method more accurate (approaching 5%), but question of precision remains (do we have poorly understood systematics?)

  7. photon calibrator injected lines • Single test in EX made at LHO ~9h prior to S4 • 5 calibration lines briefly injected • Calibration for these five curves: standard, official method

  8. response to photon calibrator • Displacement equivalent noise of photon calibrator calibration peaks (scaled by size of excitation) • Calibration here is obtained via official method • Peak displacement due to photon calibrator falls like 1/f2

  9. Comparison: official calibration vs photon calibrator • Magnitude of response functions in strain/rtHz is shown for two different calibrations • red blocks: ‘official’ • blue diamonds: photon calibrator • Good agreement (one to nine percent) PRELIMINARY

  10. Matlab models: L1

  11. H1, Seg 17, 60 sec Warm-up ~-0.3 rad “systematic error” in G0 at 1144 Hz, ~0.2% “statistical error” in ab estimate http://ligo.phys.lsu.edu/sung/Factors/S4/index.html

  12. H1, Seg 17, 16 Hz Noise bursts Gain fluctuation ~-0.3 rad systematic error ~5% statistical error

  13. Calibration dropouts • For first 3 weeks in S4: • L1: 83 instances, 283 sec flagged • H1: 56 instances, 168 sec flagged • H2: 120 instances, 360 sec (0.02%)

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